you have to boot from the windows xp cd
1) At the Welcome to Setup page, press ENTER
2) Press F8 to accept the Windows XP Licensing Agreement.
3) If an existing Windows XP installation is detected, you are prompted to repair it. To bypass the repair, press ESC.
4) All existing partitions and non-partitioned spaces are listed for each physical hard disk. Use the ARROW keys to select an existing partition, or create a new partition by selecting the non-partitioned space where you want to create a new partition. You can also press C to create a new partition using non-partitioned space.
5)To create the partition with the maximum size, press ENTER. To specify the partition size, type the size in megabytes (MB) for the new partition, and then press ENTER